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Defects of AlN ceramics with a thermal conductivity from 102 to 216 W m À1 K À1 are investigated using electron spin resonance (ESR). Two ESR signals at g ¼ 2:006 and 1.999 are related to thermal conductivity. The g ¼ 1:999 signal intensity increases with a decrease in thermal conductivity, an increase in oxygen concentration, and an increase in Mg concentration. The g ¼ 1:999 signal is tentatively supposed to be caused by an electron-trapped center. The g ¼ 2:006 signal intensity is increased with an increase in thermal conductivity, a decrease in oxygen concentration, and an increase in Ca concentration. A defect responsible for the g ¼ 2:006 signal is assigned as a hole trapped in an O N -V Al complex.

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